Based on the period age-specific fertility rate,this paper has proposed an estimation method of the cohort age-specific fertility rate and uses data of the birth cohort of 1950-1981 to explain its feasibility and reliability.This method can be applied to analyze the pattern of parity progression and related issues,particularly for the adjustment of Chinese family planning policy.Using this method,this paper has estimated the quantity and structure of women with one child,and women who are allowed to have two children by the current family planning policy but have had only one child.This would have implications for family planning policy research.